Monosodium glutamate

C 5
H 8
N 1
O 4
Na 1

19 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; monosodium glutamate has no molecular shape.

IUPAC name: sodium (2S)-2-amino-5-hydroxy-5-oxopentanoate
Molar mass: 169.112(18) g/mol
Atoms: 19
SMILES: C(CC(=O)O)C(C(=O)[O-])N.[Na+]
InChIKey: LPUQAYUQRXPFSQ-DFWYDOINSA-M
PubChem CID: 23672308

Made of

Food makers use monosodium glutamate (MSG) as a flavour enhancer. The US Food and Drug Administration (FDA) describes it as the sodium salt of glutamic acid, one of the common amino acids.

Its IUPAC name, built on the naming rules of the International Union of Pure and Applied Chemistry, is sodium (2S)-2-amino-5-hydroxy-5-oxopentanoate. Five carbon atoms form a chain with an amino group on the second and an acid group at each end, one of them written in ionised form. ChEBI, the Chemical Entities of Biological Interest database, names that anion L-glutamate(1−), and one sodium ion balances its single negative charge. Its molar mass is 169.11 g/mol.

European food-additive specifications describe the salt as white crystals or crystalline powder with practically no smell. The Medical Subject Headings (MeSH) thesaurus files MSG among the flavouring agents that lend food a meat-like flavour. MSG also makes the mouth water, and it usually dulls the flavour of sulfur-containing compounds.

Structure and bonding

The drawing shows 19 atoms in two unbonded pieces. One is a sodium ion carrying +1. The other is the glutamate ion, a five-carbon chain whose second carbon holds an NH₂ group. Next to that carbon a carboxylate is drawn: one oxygen double-bonded, the other single-bonded with the −1 charge. The far end keeps its hydrogen as –COOH.

That is one way of writing the ion. Why a carboxylate can be drawn two ways is set out for sodium acetate, and how an amino acid’s charges shift with pH for glycine. The pair is also one formula unit of an ionic lattice, the arrangement the chemical bonding article describes.

The monohydrate, with one water molecule per formula unit, crystallises from water as rhombic prisms or needles. Below −8 °C a pentahydrate, with five water molecules per formula unit, forms instead, which loses water in air and becomes the monohydrate. MSG dissolves freely in water but hardly at all in ethanol, ether or oils, the behaviour of ionic solids in most non-aqueous solvents. Its optical rotation changes sign: slightly to the left in water, to the right in acid, as for the free L-acid.

Where it turns up

FDA counts tomatoes and cheeses among the foods in which MSG occurs naturally. Free glutamate and sodium also come together in yeast extract, autolysed yeast, soy extracts, protein isolate and hydrolysed vegetable protein. On labels, FDA requires added MSG to appear in the ingredient list as “monosodium glutamate”, never as “spices and flavoring”. A food made with those ingredients may not carry “No MSG” or “No added MSG”.

Of MSG use in 1983, processed food took 30 per cent, soups and institutional buyers 25 per cent each, and direct sales to consumers 15 per cent. Beyond the kitchen, MSG has gone into US swine feed since 1963, and it improves the taste of bitter drugs. It has been used therapeutically to lower blood ammonia, and cosmetics use it as a hair conditioner.

Why it matters

In 1908, FDA recounts, a Japanese professor, Kikunae Ikeda, drew glutamate out of a traditional Asian seaweed broth and found that it gave the soup its savoury taste. That taste has a name, umami. The US National Institutes of Health’s institute for deafness and other communication disorders counts it among at least five basic tastes and calls it the taste of glutamate. Ikeda then applied for a patent on making MSG, and commercial production began a year later.

Proteins are built partly from glutamic acid, and digesting them releases free glutamate, chemically identical to the glutamate of MSG, FDA notes. The gut absorbs it through a transport system specific to amino acids. Cells of the gut lining and the liver break glutamate down so quickly that its level in blood plasma stays low after a meal. Eating MSG did not raise glutamate in breast milk, glutamate crossed the placenta poorly, and infants metabolised it much as adults do.

Properties

Properties of monosodium glutamate Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 23672308.
Property	Value	Unit	Source
Formula (Hill order)	C₅H₈NNaO₄
Molar mass	169.112(18) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	5
Hydrogen atoms	8
Nitrogen atoms	1
Oxygen atoms	4
Sodium atoms	1
PubChem molecular weight	169.11 g/mol	g/mol	PubChem

Safety

As a seasoning, monosodium glutamate is essentially harmless. FDA considers adding it to food generally recognised as safe, and it carries no hazard classification under the Globally Harmonised System (GHS) of hazard labels. Australia’s chemicals regulator places it among chemicals unlikely to need further regulation to protect health. The PubChem Laboratory Chemical Safety Summary for monosodium glutamate gathers these classifications.

Questions

Is monosodium glutamate a molecule?

No. It is an ionic compound. Its drawing shows one formula unit, 19 atoms in two unbonded pieces: a sodium ion, Na⁺, and a glutamate ion with a single negative charge. In the drawing, bonds join atoms only inside the glutamate ion, which carries an amino group and two acid groups on a five-carbon chain. A real sample is white crystals or powder, very many such ions making up a lattice.

Is MSG safe to eat?

The US Food and Drug Administration considers MSG added to food generally recognised as safe. People have reported headache and nausea after eating it, but FDA could never confirm MSG as the cause. In placebo-controlled studies of self-described sensitive people, reactions could not be triggered consistently. A 1990s review requested by FDA judged MSG safe: brief, generally mild symptoms may occur in some sensitive people who take a large amount without food. FDA considers that unlikely.

Does MSG contain gluten?

No. The names sound alike, but glutamate and glutamic acid are not gluten, FDA explains. Glutamic acid is an amino acid present naturally in the human body and in many foods. Someone with coeliac disease may react to wheat that a soy sauce can contain, but not to the MSG itself.

How is MSG made?

According to FDA, MSG is made by fermenting starch, molasses, sugar beets or sugar cane, much as yogurt, vinegar and wine are made. In the process the Hazardous Substances Data Bank records, the bacterium Micrococcus glutamicus acts on a carbohydrate, and the glutamic acid formed is then partly neutralised. Earlier, MSG was extracted from seaweed broth and crystallised, and older processes broke down beet-sugar waste liquor or wheat and corn gluten.